Electronic relay arrangement



g- 3 1948. N. R. DAVIS I 2,448,422

ELECTRONIC RELAY ARRANGEMENT Filed April 16, 1946 4 Sheets-Sheet 1 ATTORNEYS Aug. 31, 1948. RDAVIS 2,448,422

I ELECTRONIC RELAY ARRANGEMENT Filed April 16, 1946 I 4 Sheets-Sheet 2- INVENTOR WM ATTORNEYS Aug. 31, 1948.

Filed April 16, 1946 N. R.- DAVIS ELECTRONIC RELAY ARRANGEMENT 4 Sheets-Sheer) 5 INVENTQR ATTORNEYS Au .-31, 194s. R M 2,448,423 ELECTRONIC RELAY ARRANGEMENT I Filed April 16; 1946 4 Shgets-Sheec 4 JVeI/iZZe 2mm;

ATTORNEYS Patented Aug. 31, 1948 UNITED STATES PATENT OFFICE 2,44s,42a ELECTRONIC RELAY ARRANGEMENT Neville Ryland Davis, Bisham, England, assignor to Sun-Vic Controls Limited, London, England,

a company of Great Britain Application April 16, 1946,,Ser'ial No. 66252 In Great Britain May 7, 1945 relay arrangement the mean output of which, isa function of the magnitude of a controlling quantity such that the current flowing in the output circuit may be large in relation to the current produced directly inan input or controlling circuit in dependence on said controlling quantity, and which may, when desired, be made sensitive" tosmall variations of said controlling quantity. The arrangement according to the inventionis, for example; eminently applicable in the control or regulation of temperatures or other quantities in industrial or other processes, although it is to be understood that the invention is in no way limited in these respectsbut has general application for the purpose just above broadly set forth.

According to the present invention, an electronic relay arrangement for the purpose above set forth comprises a discharge device of the gaseous'conduction kind having its anode circuit energised or adapted to be energised from a source of alternating voltage, and having a.

control element connected in a control circuit producing a component of voltage dependent on the magnitude of a controlling quantity and including means dependent on anode conduction of said device for changing the resultant effective voltage produced in said control circuit in the sense to cause extinction and firing of the device in response to firing and extinction, respectively, of said device, and time delay means for modifying change of said resultant efiectivewoltage,

whereby anode conduction of said device will be periodically initiated and continued for a numb'er of cycles of alternating anode voltage of the device dependent on the magnitude of said controlling quantity, so that the mean anode current of said device in each period of conduction followed' by non-conduction will be proportional to or otherwise dependent upon the magnitude of said quantity. 7

More specifically, the electronic relay arrangement comprises a gaseous conduction discharge device having its anode and cathode connected or adapted to be connected in an alternatingcurrent circuit to be controlled by'the relay arrangement, with a control electrode or element of said discharge device connected or adapted to'be connected with acontrol apparatus to receive from the latter a variable input or controlling quantity controlling the initiation of anode conduction in 's'ai'ddevic'e, incombination with meansrespond ing with' time delay to said anode conduction arranged to produceon said control element a change of voltage such thatsaid anode conduc tion, after initiation in dependence on the magnitude of said input or controlling quantity, will continue for a number of subsequent cycles of the anode voltage dependent on the magnitude of said controlling quantity. The arrangementaccording to the i'nvention' therefore provides an electronic relay in which a load device in the anode circuit is energised intermittently at a periodicity corresponding with azplurality of cy-- cles of the alternating voltage applied to the anode of the discharge tube with the percentage time during each such period for which said current flows proportional to, or otherwise varyingin manner dependent on the magnitude of, the controlling quantity, between limits of the latter.

The electronic relay arrangement. according. to the invention is useful for example in temperature' and other regulating systems where the controlling quantityisdependent upon departure of a regulated temperature or other quantity from a desired constant or arbitrary or otherwise variabl'e value, and the discharge tube: has. connected in the anode circuit thereof, a load device com.- prising means for producing an: restoring eflect on the magnitude of said temperature or quantity. The arrangement according tothe invention is, however, applicable to any other kind of controlsystem in which the mean output current is desired to be a function of the magnitude of a controlling or input quantity,

The means responding with" time delay to the anode conduction of the gaseous conduction discharge device may for example conveniently comprise a resistance/capacity network or combination;

The response of the relay arrangement to the controlling quantity may be obtained, according toone' arrangement, byincluding in the control circuit for thegaseousiconduction discharge device an input impedance connected or adapted to be-connected with control apparatus for producing across-said impedance 3; control voltage for the relay arrangement, or,. according: to another arrangement, by including in said control circuit a control impedance which is-itself variable in response to acontrolling quantity for the relay arrangement. 7

According to another feature of the invention, the means responding with time delay to anode conduction of the gaseous conduction discharge device are connected in the control circuit of the latter so as to produce 011 the control element thereof a voltage tending to prevent said anode conduction, acting in opposition to a voltage component applied to said control element in accordance with said control quantity for initiating anode conduction of the gaseous conduction discharge device. For example, said time delay means may be. connected across the anode and cathode of said device so as to respond to asymmetry of the positive and negative halfcycles of the anode voltage of said device. alternative arrangement producing equivalent results, the means responding with time delay to anode conduction of the gaseous, conduction discharge device are arranged to produce in the control circuit of said device a voltage component tending to maintain said anode conduction, and said control circuit includes means for producing on the control element of said device a voltage component tending to prevent anode conduction of said device after extinction of the latter, said voltage produced in response to anode conduction of said device falling during said conduction so as to produce on said control element the'change of voltage resulting in termination of said anode conduction. For example, the time delay means may in this arrangement comprise a capacitance included in a rectifying circuit connected for energisation in accordance with the anode/cathode voltage of said device. In a preferred arrangement of this kind the control circuit of the gaseous conduction discharge device includes also a capacitance in series with means. for applying to the control element of said device an alternating voltage of a phase adapted to prevent anode conduction of said device, this capacitance being chargeable during non-conduction of said device to produce on said control element a uni-directional voltage component tending to maintain non-conduction of said device.

According to another feature of the, invention, the electronic relay means includes in combination with the discharge device a controlling apparatus adapted to govern the magnitude of a controlling component of voltage on the control element of said device, which controlling voltage component is an alternating voltage in, quadrature,v or otherwise phase displaced, preferably by alarge amount, with respect to an alternating biasing voltage, .which latter voltage will usually be of constant amplitude. This arrangement has the advantage that whilst the biasing voltage will be relatively large in order to be capable of preventing anode conduction during the whole of the alternating cycle applied to the anode of the discharge tube and will be in counterphase or substantially in counterphase with said anode voltage, the quadrature controlling component of .voltage may be small, for example, may have a maximum amplitude of onlyone-tenth that of the biasing voltage since said component will have its maximum value tending to initiate anode conduction when the biasing voltage is zero, or is of only low value. The arrangement can therefore be made sensitive to small variations of the controlling component of voltage and thus of the controlling quantity. The controlling voltage component may, without departing from the scope of this feature of the invention, be a unidirectional voltage, similar considerations as regards sensitivity to those above set forth then also applying, but in general the use of an alternating voltage will be more convenient.

The alternating biasing voltage may conveniently be applied to the control element of the In an" Cal discharge device directly such as from a suitable transformer, from the supply for the anode, or by being fed into the anode circuit of an amplifying thermionic valve through which the controlling voltage is applied to the control element of the gaseous conduction discharge device, so as to produce a ripple on the controlling voltage derived from said valve.

According to a further feature of the invention, where the control voltage component is an alternating voltage in quadrature or otherwise phase displaced with respect to an alternating biasing voltage, the controlling apparatus includes, or is coupled with the relay arrangement through, a circuit arrangement tuned or adapted to be tuned to the frequency of the alternating input voltage and applying to the relay arrangement a voltage which is phase displaced from, preferably being in quadrature or substantially in quadrature with, the voltage of an alternating current source from which said control voltage component is derived under control of the control apparatus.-

Conveniently the tuned circuit just above referred to may be a series resonant circuit connected or adapted to be connected with the controlling apparatus to receive current therefrom whilst the control voltage component for the control element of the discharge device is derived from a reactive element of said resonant circuit. In a preferred arrangement the reactive element comprises the primary winding of a transformer of low resistance in series circuit relation with a capacitative element, the secondary Winding of said transformer being connected in a circuit controlling, directly or indirectly, the voltage in the control element of the gaseous conduction discharge device.

The invention will now be described by way of example with reference to the accompanying drawings, in which:

Fig. 1 is an electrical circuit diagram of one embodiment of the invention,

Figs. 2, 3 and 4 are diagrams with reference to which the operation of the arrangement of Fig. 1 will be described,

. Fig. 5 is an electrical circuit diagram of a further embodiment of the invention,

Figs. 6 and 7 are curves explaining the operation of the arrangement of Fig. 5,

Fig. 8 is a curve showing a regulating characteristic which may be obtained with arrangements according to the invention,

Fig. 9 is an electrical diagram illustrating a -modification of the arrangement of Fig. 5.

Fig. 10 is an electrical diagram showing the arrangement of Fig. 5 and a control circuit therefor.

The arrangement shown in Fig. 1, which will be assumed by way of example to be employed for the temperaturecontrol of an electrically heated furnace or other enclosure, although applicable for any other desired regulating or con trol purposes, comprises a gaseous conduction discharge device I of the kind known as a thyratron in combination with a thermionic amplifying valve 2 and a controlling apparatus which is indicated generally at 3.

In the embodiment of the invention being described the controlling apparatus 3 comprises a resistance thermometer 4 connected as one arm of a Wheatstone bridge in conjunction with fixed resistors 5, 6 and I. This Wheatstone bridge is energised either directly or, as in the example shown, through the transformer 8, from a suitable source of alternating current at 9, such as the usual supply mains. The primary winding 10 of .an 1 input transformer 5 H Ifor the ;..-thermion.ic valve 2 is connected. in. series with: a capacitance l2 acrossthepoutput points of the Wheatstone bridge. The capacitance I2 is given such value in relation: to the. ihrliictanceof .the primary winding IED-as to tune-theslatter tothefrequency of thesource 9. .Eurthermore the transformer II is designed so .that the ratiocof inductanceto resistance of the winding I'Ois high. The transformer has a secondarywinding 1 l3 which is connected through-a current-limiting resistor; M with the-controlgrid of the'valve 2, said-valve being a pentode as shown, or, alternatively, a tetrode. The cathode of thevalve is'connected, through a resistor l5: providing automatic grid bias in well known manner,'with a negativebusbar lfi -which-is connected .with one end of a secondary winding I! of a transformer 18 "for supplyinganode current to the gaseous conduction tube |,.as will hereinafter be described in:more detail. The primary winding IQ of the transformer i8 is connectedwith theisource .9uas-inidicated at 9' and saidtransformer is provided with secondary winding which, in accordance with-.usual practice, supplies: heatin current to :the operating element-:21 of a thermal time delay relay 22, the contacts of which control the circuit of the winding'l'l sorthat'the high tension voltage will not be applied to'the anode of the thyratron until the cathode thereof has reached the normal operating temperature, it being understood that the vicathodeiheaters ofboth the thyratron and the pentode or tetrode :2 are in the msualuway energised fromthe winding $20 or a further secondary winding of the transformer 18. The other end of the secondary Winding l3 of :theinputitransformerfl -.is connected with the'negative' busbar t6;.a decoupling capacitance '25 may be connected between this end of .the

winding l3 and the cathode of the Valve-2in accordance with usual practice.

The anode circuit of the valve 2 is energised from .a suitable source of direct current applied between the negative busbar IE on the one hand and a positive lead .25on the other hand. This conductor 25 is, for a purpose which will hereinafter appear, connected with one end of .a potentiometer resistance '26, to which there is applied by means of a transformer '21 an: alternating voltage from and inphase with that of the source 9 as indicated at 9". The variable tapping point 28 of the potentiometer is connected through an anode resistor 29 and a decoupling resistor 30 with the anode of the valve 2. 'The value of this decoupling resistor is large in rela- -tion to the anode resistance in the valve'2. The

anode circuit of the valve 2 is resistance/ capacity coupled with the grid or input'circuit of the thyratron by means of the anode resistanceZB,

a capacitance 3|, and a resistor32 forming-the;

input orcontrol impedance of the thyratron control circuit. The resistor '32, instead of being :connected directly with'the negative busbar 16, is connected with said' busbar through a capacitance 33 which, as will hereinafter betexpla'ined,

constitutes. the terminal element of a time delay network, and in view of its function as hereinafter described may convenientlvbe referred to was the timing capacitance. The grid of the thyraitron is connected withthe capacitance?) I through :a .grid current limiting resistor 34.

The anodecircuit of the thyratronincludesgin addition to aifixedresistor 3B,:the operating element of. asuitable contactor for control-lingthe 'heat i-nputto theturnace'; i-n the example show-n is therefore zero.

this. contactor comprises a thermal vacuum relay of :which the heating element is. shownatQland the contacts at..38. .Itwill-beunderstoodthattthe contacts 38.may be connected in circuit withan-y desired means for controlling." the heat input .to the furnace. For example said contacts may .zbe connected directly in circuit with the :heatin elements wherethe furnace is :of the electrically heated kind. As shown the thyratron-is preferably .a tetrode- 'A:potentiometerresistance 39 is connected between the anode of the thyratron and the; nega tive::busbar-l6. The variable tappingpoint. of this potentiometer is connected with the input of the time delay network hereinbefore referred to,-;which network comprises two resistorsll'i and 42 inconjunction with a capacitance 43 and with the timing capacitance 33.

Preferably the anode resistance'29 and-decou pling resistor 30 of the valve 2 are shunted bye. capacitance 44 in serieswith a resistor element 45, the resistance of which falls with increaseof applied voltage, this arrangement operating to limit the output voltage of the amplifying valve as hereinafter explained.

In the operation of the arrangement 'showni-n Fig. 1, the pentodc or tetrode 2 will apply to the control grid of the thyratron I avoltage-comprisingtwc components. The first component, which will be referred to as the control component, is derivedfrom the variation of anode current of the valve 2 in dependenceupon the alternating control grid voltageof said valve derived from the Wheatstone bridge 3. The second component, which will be referred to as the :anti-phase 'component, is an alternating component injected into the anode circuit of the valve-2 from the potentiometer 26. The primary winding of the transformer. 2lis connected with the supplysource at 9" in such direction that the. corresponding alternating voltage componentapplied to-the grid of the thyratron is in phase opposition to the voltage applied :by secondar winding ll of transformer I8 to the anode of the-thyratron. The potentiometer 25 is adjusted'so that the magnitude of .the anti-phase component applied toathe grid of ,3 is-balanced, and'the voltage'applied to the primary winding IU of the input transformer These conditions are represented in Fig. 2, in which the curve A shows one cycle of the anode voltage on the thyratron and the curve I the anti-phase component of .grid voltage derived from the transformer 21-and potentiometer 26-;- at thisitime the anti-phase voltage 'constitutes'the resultant voltage applied to the grid ofthe thyratron. It will be understood that in these circumstances the heating element 31 :01? the vacuumswitch remains de-energised so that there will be no heat input to the furnace.

Assuming now that the temperature of "the furnace is such that thebridge'3 is unbalanced, then thealternating voltage appearing across the output points of said bridge will cause an alternating current to flow in the tuned circuit comprising capacitance I2 and winding [9, and since this circuit is tuned and thewinding H] has a "large ratio of inductance to resistance, a comparatively largevoltage-will be produced in the secondary winding 13 of the input transformer and and the anode voltage of-the thyratron. Theatrangei'nent is such that the input voltage will lag with respect to the thyratron anode voltage upon unbalance of the bridge due to the furnace temperature being below a predetermined value at which the bridge is balanced; the amplitude of said input voltage will be dependent on the extent to which said bridge is unbalanced and therefore on the extent to which the furnace temperature falls below said value at which the bridge is balanced. The voltage derived from the bridge is amplified by the pentode and applied to the control grid of the thyratron superimposed on the anti-phase component derived from the potentiometer 26 from the transformer 21. a As explained above, the secondary voltage of the transformer leads the current in the tuned input circuit by substantially ninety degrees, so that the control component of voltage is substantially in quadrature with both the anode voltage and the anti-phase voltage. These conditions are shown by Fig. 3, in which the curves A and I again represent the thyratron anode voltage and the antiphase component of the grid voltage, whilst the curve C represents the control component of voltage derived from the valve 2 lagging in quadrature the control component I, giving a resultant grid voltage of the thyratron as shown by the curve B. This resultant voltage is, assuming a sinusoidal supply voltage, also a sinusoidal voltage, but its phase with respect to the anode voltage of the thyratron will depend upon the magnitude of the control component since the latter is in quadrature with the anti-phase component. As will be understood a small variation in the amplitude of the control component will be sufficient to effect a substantial displacement of phase of the resultant grid voltage since the control component is in quadrature with the anti-phase component of grid voltage and, for example, a maximum control component of one volt will provide the required operation in conjunction with an antiphase component of the order of ten volts.

The arrangement is such that a reduction of the regulated temperature will retard the phase of the resultant thyratron grid voltage, and assuming the voltage derived from the bridge has sufficient magnitude the thyratron will fire at or near the beginning of a cycle as represented by the line F in Fig. 3, with consequent conduction of anode current for substantially the remainder of the cycle as represented by the hatched area in Fig. 3. The vacuum switch or other contactor is therefore operated to close its contacts and apply heating current to the furnace to tend to raise the temperature thereof. It will be understood that in the absence of further operation the heating current would under these conditions be applied to the furnace during each cycle of the alternating voltage. By the employment of a vacuum switch for controlling the heatin cur rent of the furnace, or by equivalent means operating with a time delay, the heating current may be supplied without interruption in spite of the termination of thyratron conduction during alternate half-cycles.

There is applied to the grid of the thyratron a further component of voltage which is derived from the potentiometer 39. Since this potentiometer is connected between the anode and cathode of the thyratron it will be clear that the voltage across said potentiometer will, when the thyratron fires, be less than during the negative half-cycle of the anode voltage When the anode current is zero. As a result a negative Voltage will build up on the timing capacitance 33 of the time delay network 4|, 42, 43, 33, and furthermore said voltage will build up at a rate which is dependent on the values of the capacitances and resistors of said network and the setting of the potentiometer 39. The result is that when the thyratron has conducted anode current for a sufficient time to cause this further biasing voltage to neutralise the effect of the input voltage, producing the conditions shown in Fig. 4, in which there is added to the resultant voltage R of Fig. 3 a uni-directional component N derived from the capacitance 33 producing the resultant grid voltage R, the thyratron will not fire at the commencement of the next cycle so that the vacuum switch will reopen its contacts and the heating current to the furnace will be interrupted.

In consequence of the termination of thyratron conduction the mean voltage applied to the potentiometer 39 is zero since the voltage applied to said potentiometer is now the same during each half-cycle of the anode voltage. Consequently the voltage appearing across the capacitance 33 will gradually disappear and a condition will again be reached at which the voltage derived from the input transformer 21 in the anode circuit of the valve 2 will be able to initiate firing of the thyratron and the cycle of operations above described will thus continue.

Due to the exponential chargingand discharging voltage curves with respect to time of the timing capacitance in the time delay network the proportion of each cycle of operations during which the charge from said capacitance is being increased and reduced will depend upon the input voltage, that is to say upon the magnitude of the quadrature component derived from the transformer I3 so that the proportion of time for which in each cycle of operation heating current is supplied to the furnace will depend upon the temperature of the furnace. This aspect of the operation will be sufficiently understood by those skilled in the art, but is also described in more detail with reference to Figs. 6 and '7 in connection with Fig. 5. This proportion of time increases with reduction of furnace (temperature, so that the average heat input to the furnace is varied in the opposite sense to variations of furnace temperature, thereby to maintain the latter substantially at a desired value.

At the upper limit of regulated temperature the firing of :the thyratron is prevented in every cycle of the alternating supply voltage with continuous de-energisation of the furnace whereas at a given lower limit of furnace temperature the quadrature or control component of thyratron grid voltage is sufficiently great that the voltage derived from the potentiometer 39 will never become sufficient to terminate the anode conduction of the thyratron, so that the latter fires in every cycle of the alternating supply voltage and the furnace is continuously energised. Between these limits the average energy input to the furnace is continuously variable in response to variation of furnace temperature. The arrangement enables the energy input to the furnace to be varied over the whole range between said limits, namely from continuous de-energisation to continuous energisation by a small variation in the magnitude of the furnace temperature, with correspondingly sensitive and accurate regulation of the furnace temperature to (the desired value. By a suitable choice of the parameters of thetime delay network the duration of the complete cycle of operations of the vacuum switch can be selected appropriately to the particular application of the invention. It-is contemplated for example that in one particular application of the embodiment shown in Fig. 1 said periodmay be of the order of sixty seconds.

The well-known anode current/anode voltage characteristicof rthepentode or tetrode as employed for the amplifying: valve 2 has the advantage that the grid voltage of the thyratron derived from the transformer" 21 will not be unduly reduced by the anode-cathode path of said-valve inparallel with the coupling capacitance .31. and coupling resistor 32.

The capacitance 44 and'resis'tor 455 operate to limit the magnitude of the quadrature component which may be'appli'ed to the grid of the thyratron, so that the phase of the resultant alternating voltage on said grid can never be displaced by more than ninety degrees from the anti-phase relation to the anode voltage of the thyratron irrespectively of the extent to which the bridge is unbalancedi In practice the phase displacement will be limited toa lesser amount than ninety degrees. The resistor 45 may be one of the well known materials having the resistance/voltage characteristic hereinbefore referred to.

.It will be understood that the specific arrangement of thyratron-and grid circuits thereof as above described maybe employed in combination with other controlling means than the amplifying valve above described, and that the combination'of thyratron and amplifying'valve with their input circuits as specifically describedabove may be employed in conjunction withother means producing a desired input voltage than those specifically described, for obtaining response to any desired quantity.

In some particular applications of the arrangement'shown in Fig. 1 some interference with the desired operation may'result from the fact that the timing capacitance 330i Fig. l tends to be charged by the grid current of the thyratron during the positivehalf-cycles of thyratron anode voltage when the thyratron is not firing and to be so chargedin the sense to apply a-negative potential to the grid. Fig. 5 shows amodification of the arrangement whereby this objection may be avoided, the arrangementof Fig. 5 including-a rectifier in the charging circuit of the timing capacitance and beingsuch that the voltage derived from the anode circuit of the thyratron applies to the timing capacitance, through said rectifier, a charge in the sense to apply a positive potential to the thyratron grid during the positive half-cycles of thyratron anode voltage whilst the negative halfecycles ofanode voltage are ineffective to modify the charge on-the timing capacitance. This charge will balance the negative charge which the timing capacitancetends to receive from the thyratron grid and when the charge derived across the timing capacitance from'the thyratron anode circuit-sufliciently exceeds that due to'the'grid current the thyratron will ultimately fire. The consequent reduction of thyratron anode-cathode voltage drop on the positive half-cycles will then' allow the positive charge on'the timing capacitance to fall so that the thyratron is extinguished whereupon positive voltage on the timing capacitance again builds up to repeat-the-above described cycle of operation. In order that the period-of operation may be'made of sufficient duration and regularity means are also provided whereby a negative voltage component is: appliedrtothe grid. during the non conduction of the 'thyratroniso that to aextim.

10 guish the thyratron the voltage on the timing capacitance must fall. toa considerably lower value than that necessary to initiate firing. As will be explained in more-detail hereinafter'the arrangement is controlled by the application of i a control component of voltage to the grid circuit of the thyratron, which control voltage determines the valuesof voltage of the timing capacitance necessary to initiate and terminate firingv of the thyratron so that. due to the exponential charging and discharging voltage-time curves of the timing capacitance with respect to timethe percentage timein each cycle of operation for which the thyratron fires will vary with the mag nitude of said control voltage in similar manner to that obtained with the-arrangement of Fig. 1.

In Fig. 5 the thyratron is .again shown at l, the vacuum relay or other controlled device is shown at 56, connected in the anode circuit of the thyratron for energisati'on from the anode supply secondary Winding l l-of-the transformer 3; The thyratron grid is connected through. a. grid cur rent limiting resistor 34 with a capacitance5l shunted bya-resistor 52, the grid circuit including also in series circuit relation a-resistor 53 forming the input or control impedance of the thyratron control circuit which resistor- 53 may be the resistor 32 of Fig. 1; afurther secondary winding 54 of the transformer l8-and the timing capacitance 33. The timing capacitance is -con* nected, in series'with-a' resistor 55; between the cathode of the thyratron and the-variabletapping point N! of a potentiometer '39, which po tentiometer, as 'in Fig. 1 is connected between the anode and cathode orthe-thyratrombutin the arrangement of Fig. 5'has connected inseries therewith a dry-platerectifier 56-which allows current to flow in thepotentiometer only during the positive half-cycles of anode voltage.

The input resistor 53 is'connectedwith any desired means producing thereon: a control voltage which is-representative'of some condition on the magnitude of which .it isdesiredthat the average anode current of the thyratron, and therefore the average: value of some controlled quantity, shall depend. Preferably this input voltage is either derived from adirect current source or is an alternating voltage in quadrature or substantially in quadrature with'the voltage produced by the winding 54-, although it could be an alternating voltage in phase or anti-phase with the voltage" of winding 54. The first mentioned arrangements are in general preferred since the last mentioned arrangement has the disadvantage that a much larger amplitude of the control voltage is required, for the same reasons as describedin connection with Fig. 1.

The operation of the arrangement of Fig. 5 will first be described for a case where'theinput voltage is derived :from'a direct current source. Fig. 6 is a set of curves of the various components of grid voltage plotted on the ordinates against time, and shows the operation :during one cycle of'operation, extending over a plurality of cycles of the anode voltage, for exampleextcnding over three thousand such cycles of anode voltage. The horizontaldine'c in -Fig; 6 represents a negative control 'voltageof a given-magnitude. At the commencement'of the cycle, at time t1, the thyratron iscxtinguished so that the voltage of the secondary winding 54 will cause current to flow between the grid and cathode of thexthyratron during alternate "half-cycles of the supply voltage, that'isto say'during thehalf- 11 cycles when the voltage in winding 54 acts downwardly in Fig. 5; on the other hand current will not flow from the winding 54 during the other half-cycles. As a result the capacitance 5! will be charged in the direction to app-1y a negative potential to the grid, and this negative voltage on capacitance 5| will have a magnitude determined by the values of the several resistances in the grid circuit. The resistance/capacitance combination 52-5l is arranged with a short time constant, for example less than 0.1 second, so that the capacitance 5| comparatively rapidly reaches a steady voltage, said time constant, however, being sufficiently great that the capacitance will hold its charge for a few cycles of anode voltage. This rise in negative voltage on the capacitance 5| is shown at a in Fig. 6 increasing the resultant negative voltage on the grid from the line a to a value equal to the sum of the control voltage and the voltage a on the capacitance Simultaneously the voltage across the capacitance 33 will rise, since at the end of the preceding cycle of operations the thyratron has been conducting so that the anodecathode voltage thereof had a low value, but upon extinction of the thyratron at time t1 the increase of anode-cathode voltage substantially to the anode supply voltage of the secondary winding U will commence to charge the capacitance 33 through the rectifier 56 during the positive halfcycles of anode voltage. The time constant of the resistance/capacitance combination 55-33 is made considerably greater than that of the combination 525| for example is about ten seconds. The voltage across the timing capacitance 33 therefore commences from whatever voltage re mained at the commencement of the cycle of operation and rises comparatively slowly as shown by the curve b toward the final steady state voltage E of the capacitance. When the voltage across the capacitance 33 has risen surficiently to neutralise the sum of the voltages across the capacitance 5| and that across the resistor 53, that is has risen to a value somewhat in excess of the sum of the voltages c and a, the thyratron will fire, namely at the time 252. The load 50 is therefore energised during following halfcycles of the anode voltage. Due to the fall of the anode-cathode voltage drop to a low value the timing capacitance 33 is no longer charged through the rectifier 56 but discharges through the resistor 55 so that the voltage across said capacitance falls as shown by the curve 12'. This fall of voltage on capacitance 33 does not, however, immediately extinguish the thyratron, because as a result of the firing of the thyratron at time 152 the fall of grid-cathode resistance causes immediate disappearance of the negative charge on the capacitance 5| so that the voltage a is removed and the grid voltage becomes the voltage 0. Furthermore, the winding 54 is now efi'ective to apply an alternating voltage component to the grid in anti-phase to the anode volt age. The ratio of anode voltage from the winding I! to the grid voltage from the winding 54 is made less than the gas ratio of the thyratron, that is to say less than the ratio just sufficient to fire the thyratron in the absence of other components of grid voltage. The grid voltage is thus I now determined by the voltage of the timing cato the anode voltage so that it is zero at the commencement of the cycle and does not prevent firing of the thyratron so long as there is a sufficient resultant positive component of voltage on said grid at the instant in each positive half-cycle of anode voltage at which the anode voltage reaches the anode-cathode voltage drop of the thyratron.

The grid voltage is therefore sufiicient to fire the thyratron at each succeeding positive half cycle of anode voltage until the timing capacitance has been discharged to a voltage substantially equal to the control voltage 0. When this occurs the thyratron is extinguished, namely at time ta and the above described cycle of opera tions is repeated. Thus the capacitance 5| is again rapidly charged negatively in accordance with the line a whilst the timing capacitance 33 is charged and discharged comparatively slowly according to curves b and Z).

From the above description it will be clear that the arrangement operates to fire the thyratron for alternate periods each including a plurality of cycles of the alternating anode voltage, with the intervening periods in which the thyratron is extinguished also each including a plurality of cycles of said anode voltage. As will now be described, the ratio between the duration of the firing periods to the duration of the extinguished periods, that is to say the percentage firing time, is varied by variation of the control voltage.

Assuming that the magnitude of the negative input voltage is increased to the value shown by the horizontal line 0' in Fig. '7, then at the time ii, that is to say at the end of the preceding cycle, the thyratron is extinguished at a higher value of voltage on the timing capacitance 33 than is the case in Fig. 6. The voltage across the timing capacitance then rises less steeply than in Fig. 6 due to the exponential form of the charging curve. A longer period therefore elapses between the time h and time 152 at which latter time the timing capacitance voltage is suflicient to overcome the sum of the voltage a and the increased voltage 0 to cause firing of the thyratron. The fall of the voltage across, the timing capacitance as the latter discharges is moreover more rapid than in Fig. 6, again due to the exponential form of the discharging curve, so that the resultant grid voltage drops more rapidly from the Value substantially equal but opposite to the sum of the control voltage 0 and the voltage a produced during extinction of the thyratron on the capacitance 5| to the value of the control voltage. Consequently the number of cycles of anode voltage during which the thyratron fires is reduced and the number of cycles during which the thyratron is extinguished is increased thereby to reduce the resultant percentage time of firing.

In the limit, when the control voltage is made substantially equal to the difference between the steady state voltage E of the timing capacitance 33 and the steady state negative voltage a. produced on the capacitance 5|, the thyratron will be continuousl extinguished. If the control voltage is reduced to zero the duration of the periods of extinction becomes still shorter than in Fig. 6, the voltage across the timing capacitance being required then to vary only between substantially zero and a value substantially equal and opposite to the voltage a in Figs. 6 and 7. If the control voltage is reversed so as to act in the same direction as the voltage across the timing capacitance then the percentage time of firing is increased still further until in the limit when .egaesgeee 13 the control voltag is substantially equal to'the voltage a the thyratron fires continuously. It will thus be seen that the percentage time of firing is continuouslyvariable between zero and one hundred percent by variation of the control voltage; The percentage time of firing is plotted in Fig. 8 on the ordinates against the control voltage and 'it will be seen that over the major part of the range of variation thepercentage time of firingis substantially proportional to the magnitude of the control voltage.

When the control voltage is an alternating quantity in quadrature with the voltage from the winding 54 so as to control the firing by phase shifting of the resultant alternating voltage appliedto' the thyratron grid, the operation will be similar to that above described, adjustment of the phase of said alternating voltage being-equivalent' to varying the magnitude of a direct control voltage as regards'the voitages of the timing capacitance 33 at which firing will be initiated and terminated'and therefore having similar effect on the percentage time of firing;

Fig. 10 shows the arrangement of Fig. 5 con trolled by an alternating current arrangement iii-which the resistor 53' corresponds, for exampie, with the resistor 32 of Fig. l forming part of a resistance/capacitance coupling between the anode of'thevalve '2 of Fig. 1 and the thyratron grid'circuit. The valve 2 may for-example again be controlledby the means 3 of Fig. 1. The potentiometer '26 and transformer 2: of Fig. 1 are, in connection with the arrangement of Fig. 10, omitted from the anode circuit of the valve, since the anti-phase componentv of the thyratron gridvoltage, produced in the arrangement of Fig.

1 by this means, is. in-the arrangement of Fig. 5 produced instead by the transformer secondary winding 54.

Instead of the input or control quantity being derived externally and applied to the grid circuit inithe form of a voltage developed across the input resistor 53, the latter may itself be subject to variation in accordance with the desired control quantity so as to modify the voltage conditions in the grid circuit in accordance with change of said control quantity. Thus variation of the resistor 53in -Fig. 5 will modify the steady state negative voltage to which the capacitance 5| will be charged. There is then no external control voltage according to line of Figs. 6 and 7, but instead each period of thyratron extinction must be suffic-ient for the voltage on the timing capacitance 33 to rise from substantially zero to the steady state value of the voltage on capacitance that is to overcome the voltage a .of Figs. 6 and.'7, so that the durationof each period of extinction is reduced as the value of resistor 53 is increased, since this reduces the value of the voltage a in Figs. 6 and '7. when the thyratron fires, it will continue firing for a number of cycles of the anode voltage sufficient for the voltage on the timing capacitance to fallagain substantially. to zero, so that the duration of each firing period increases with increase of the value of resistor 53. Adjustment of the value of resistor 53 also has afurther effect on the-time at which the thyratron is extinguished in each cycle, since said resistor affects the resultant/phase of the voltage which is applied by the winding 54 to the grid during firing oi the thyratron. Increasing the value of said resistor retards thephase of the alternating voltage component applied to the grid during the firing of 'the thyratron; which ashereinbefore described has On the other hand,

1 4 theefiect of lengthening the firing periods. The result is, therefore, that increasing the value of resistor 53 increases the percentage time of firing of the thyratron.

It will be understood that the resistor 53cm in the application of the invention just above described be: varied in any desired manner, automatically or otherwise in response to. a desiredcontrolling quantity, and may furthermore be'aresistor which varies inherently inxresponse to said quantity, such as for example in response to themagnitude of a controlled temperature.

Of thetwo effects of the variation in resistor 53 producing-variation of the percentage time of firing, namely, the effect on the voltage to which capacitance 5| is charged and the effect of. the

quired'range of variation of the controlling quanrtity therefor, said: resistormay be included .inya suitable bridge orv like arrangement which" will render the grid circuit ofthethyratron desirably sensitive to the required small variation ofithe resistor 53. Fig. 9. shows one-such arrangement, appliedito a case where the variation of percent:- age time offiring is determined mainly by the phase shift of alternating grid voltage component by the resistor 53.

In-the arrangement. of Fig; 9, the transformer Ill. is provided withazfurther secondary winding having connected thereacross a potentiometer Bi and capacitance 62 l in series with one another. The variable tapping point of this potentiometer is connected with the'control resistor 53..and:one end of the potentiometer resistance is connected with the lower; end'of the winding 54 in the manner shown. The winding 60 produces a voltage in anti phase' to theuanode'voltage and the-potentiometer'injects into the grid circuit acornponent leading onsaid anode voltage and'adjustable' in magnitude by the setting of themtentiometer. 5!, whereby the level of controlled quantity aboutwhich'the apparatus operates may be adjusted at will.

It will be understood that arrangements of the kind illustrated by Fig 9 are applicable also in connection with the. arrangement of Fig. 1.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electronic relay arrangement comprising. agaseous conduction discharge device having an anode; acathode and a control electrode,

a controlcircuit for said control electrode in- -cluding-a capacitance and'a discharge path for extinction of the anode current, the voltage produced response toanode conduction on: the

first said capacitance falling during conduction so as to produce on said control electrode a change of voltage resulting in extinction of anode current, and means for producing in said control circuit a, controlling voltage component governing the anode conduction in said device in accordance with the magnitude of'an input quan tity, whereby periodically to initiate and con tinue anode conduction during a number of cycles of anode voltage dependent upon the magnitude of said input quantity.

2. An electronic relay arrangement comprising a gaseous conduction discharge device having an anode, a cathode and a control electrode, a control circuit for said control electrode including a capacitance and a discharge path for said capacitance, a charging circuit for said capacitance having rectifying means therein connected across the anode and cathode of said device for charging said capacitance during positive half-cycles of anode voltage to apply to said control electrode a voltage subject to time lag tending to cause anode conduction of said device, said control circuit also including a second capacitance in series with means for applying to said control electrode an alternating voltage of a phase tending to prevent anode conduction of said device, saidsecond capacitance being chargeable during non-conduction of said device to tend to produce on said control electrode a unidirectional negative voltage tending to maintain non-conduction after extinction of the anode current, and the voltage produced in response to anode conduction on the first said capacitance falling during conduction so as to produce on said control electrode a change of voltage resulting in extinction of anode current, and means responsive to the extent of departure of a regulated quantity from a desired value connectedwith said control circuit for producing in said control circuit a controlling voltage component governing the anode conduction in said device in accordance with said departure, whereby periodically to initiate and continue anode conduction during a number of cycles of anode voltage dependent upon the extent of said departure.

3. An electronic relay arrangement comprising a gaseous conduction discharge device having an anode, a cathode and a control electrode, a control circuit connected to said control circuit and including a capacitance and a discharge path for said capacitance, a charging circuit for said capacitance having rectifying means therein connected across the anode and cathode of said device for charging said capacitance during positive half-cycles of anode voltage to apply to said control electrode a voltage subject to time lag tending to cause anode conduction, said control circuit also including a second capacitance in series with means io-r applying to said control electrode an alternating voltage of a phase tending to prevent an-ode conduction of said device, said second capacitance being chargeable during non-conduction of said device to [tend to produce on said control electrode a unidirectional negative voltage tending to maintain non-conduction after extinction of the anode current, and the voltage produced in response to anode conduction on the first said capacitance falling during conduction so as to produce on said control electrode a change of voltage resulting in extinction of anode current, and control apparatus connected with said control circuit for superimposing on said alternating voltage tending to prevent anode conduction a controlling component of alternating voltage having a large phase displacement with respect to said voltage tending to prevent anode conduction, whereby periodically to initiate land continue anode conduction during a number of cycles of anode voltage dependent on the magnitude of said controlling component of voltage.

4. An electronic relay arrangement comprising a gaseous conduction discharge device having an anode, a cathode and a control electrode, a control circuit connected to said control electrode including a capacitance and a discharge path for said capacitance, e, charging circuit for said capacitance having rectifying means therein connected across rthe anode and cathode of said device ror charging said capacitance during positive half-cycles of anode voltage to apply to said control electrode a voltage subject to time lag tending to cause anode conduction, said control circuit also having a second capacitance connected therein in series with means for applying to said control electrode an alternating voltage of a phase tending to prevent anode conduction in said device, said second capacitance being chargeable during non-conduction of said deulce to tend to produce on said control electrode a unidirectional negative voltage tending to maintain non-conduction after extinction of [the anode current, and the voltage produced in response to anode conduction on the first s aid capacitance falling during conduction so as to produce on said control electrode a change of voltage resulting in extinction of anode current, and control apparatus responsive to the extent of departure of a regulated quantity from a desired value connected with control circuit for superimposing on said alternating voltage tending to prevent anode conduction a controlling component of alternating voltage dependent in magnitude on said departure and having a large phase displacement with respect to said voltage tending to prevent anode conduction, wIh-ereb-y periodically to initiate and continue anode conduction during a nurnber of cycles of anode voltage de-pendent upon the extent of said departure.

5. An electronic relay arrangement comprising a gaseous conduction discharge device having an anode, a cathode and a control electrode, a control circuit connected to said control electrode including a capacitance and a discharge path for said capacitance, a charging circuit for said capacitance having rectifying means therein connected across the anode and cathode of said device for charging said capacitance during positive half-cycles of anode voltage to apply to said control electrode a voltage subject to time lag tending to cause anode conduction, said control circuit also having a second capacitance connected therein in series with means for applying to said control electrode an alternating voltage of a phase tending to prevent IBJlOde conduction, said second capacitance being chargeable during non-conduction of said device to tend to produce on said control electrode a unidirectional negative voltage tending to maintain non-conducti-on after extinction of the anode current, and the voltage produced in response to anode conduction on the first said capacitance falling during conduction so as to produce on said control electrode \a change of voltage resulting in extinction of anode current, and an input impedance in said control circuit, whereby periodically to initiate and continue anode conduction during a number of cycles of anode voltage dependent upon the magnitude of a control voltage applied across said impedance.

6. An electronic relay arrangement comprising a, gaseous conduction discharge device having an anode, a cathode and a, control electrode, a control circuit connected to said control electrode and including a capacitance and a discharge path for said capacitance, a charging circuit for said capacitance having rectifying means therein connected across the anode and cathode of said device ct'or charging said capacitance during positive half-cycles of anode voltage to apply to said control electrode a voltage subject to [time lag tending to cause anode conduction, a second capacitance in said control circuit :in series with means for applying to said control electrode an alternating voltage of a \phase tending to prevent anode conduction of said device, said second capacitance being chargeable during nonoonducti-on of said device to tend to produce on said control electrode a unidirectional negative voltage tending to maintain non-conduction after extinction of the anode current, and the voltage (produced in response to anode conduction on the first said capacitance falling during conduction so as to produce on said control electrode a change of voltage resulting in extinction of Ian-ode current, and a variable impedance in said control circuit, whereby periodically to initiate and continue anode conduction during a number of cycles of anode voltage dependent upon the value of said impedance.

'7. An electronic relay arrangement comprising a gaseous conduction discharge device having an anode, a cathode and a control electrode, a control circuit connected to said control electrode and including a capacitance and a discharge path for said capacitance, a charging circuit for said capacitance having rectifying means therein connected across the anode and cathode of said device for charging said capacitance during positive half-cycles of anode voltage to apply to said control electrode a Voltage subject to time lag tending to cause anode conduction, a second capacitance in said control circuit in series with means for applying to said control electrode an alternating voltage of a phase tending to prevent anode conduction of said device, said second capacitance being chargeable during non-conduction of said device to tend to produce on said control electrode a unidirectional negative voltage tending to maintain non-conduction after extinction of the anode current, and the voltage produced in response to anode conduction on the first said capacitance falling during conduction so as to produce on said control electrode a change of voltage resulting in extinction of anode current, and control apparatus including a resonant circuit having a reactive element connected with the said control circuit to apply to said control circuit an alternating voltage dependent on a controlling quantity applied to said control apparatus, the last said voltage having a large phase displacement with respect to said alternating voltage tending to prevent anode conduction, whereby periodically to initiate and continue anode conduction during a number of cycles dependent upon said controlling quantity.

8. An electronic relay as defined in claim '7, wherein said reactive element comprises the primary winding of a transformer of low resistance and a capacitative element in series circuit relation therewith, and a circuit having the secondary winding of said transformer connected therein and controlling the voltage in the control electrode of said gaseous conduction discharge device.

9. An electronic relay arrangement comprising a gaseous conduction discharge device having an anode, a cathode and a control electrode, a control circuit for said control electrode including a capacitance and a discharge path for said capacitance, a charging circuit for said capacitance having rectifying means therein connected across the anode and cathode of said device for charging said capacitance during positive half-cycles of anode voltage to apply to said control electrode a voltage subject to time lag tending to cause anode conduction of said device, a second capacitance in said control circuit in series with means for applying to said control electrode an alternating voltage of a phase tending to prevent anode conduction, said second capacitance being chargeable during non-conduction of said device to tend to produce on said control electrode a unidirectional negative voltage tending to maintain nonconduction after extinction of the anode current, and the voltage produced in response to anode conduction on the first said capacitance falling during conduction so as to produce on said control electrode a change of voltage resulting in extinction of anode current, and a bridge circuit having a control impedance responsive to a controlling quantity connected therein, said bridge circuit being connected in said control circuit for producing in said control circuit a controlling voltage component governing the anode conduction in said device and dependent on the extent of departure of said quantity from a prescribed value, whereby periodically to initiate and continue anode conduction during a number of cycles of anode voltage dependent on said departure.

NEVILLE RYLAND DAVIS.

REFERENCES CITED UNITED STATES PATENTS Name Date Glass Oct. 9, 1945 Number 

